This is my take on a legendary Medusa and draws on the original Clash of the Titans film and the Yuan-Ti Malison stat-block as inspirations. The Legendary Medusa has the upper body of a humanoid female and the lower body of a great serpent, the tail of which is topped by the rattle of a rattlesnake.

Perhaps in your world all Medusa are like this or perhaps the Yuan-Ti Malison went too far in trying to increase its power and suffered the curse of the Medusa from its Serpent Lord.

How and why is up to you. I just thought this is a cool take.

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Legendary Medusa

Large monstrosity, lawful evil

Armour Class: 15 (natural armour)
Hit Points: 144 (17d10 +51)
Speed: 30ft.

Strength: 16 (+3)
Dexterity: 15 (+2)
Constitution: 16 (+3)
Intelligence: 14 (+2)
Wisdom: 13 (+1)
Charisma: 16 (+3)

Saving Throws: Constitution +6
Skills: Deception +6, Insight +4, Perception +4, Stealth +5
Damage Immunities: poison
Condition Immunities: poisoned
Senses: Passive perception 14, darkvision 60 ft
Languages: Common, Abyssal, Draconic
Challenge: 8 (3,900 xp)

Innate Spellcasting: The Medusa's innate spellcasting ability is Charisma (spell save DC 13). The Medusa can cast the following spells, requiring no material components.

At will – Animal Friendship (snakes only)

Petrifying Gaze: When a creature that can see the Medusa's eyes starts its turn within 30 feet of the medusa, the medusa can force it to make a DC 14 Constitution saving throw if the medusa isn't incapacitated and can see the creature. If the saving throw fails by 5 or more, the creature is instantly petrified. Otherwise a creature that fails the save begins ot turn to stone and is restrained. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success. The petrification lasts until the creature is freed by the greater restoration spell or other magic.
Unless surprised, a creature can avert its eyes to avoid the saving throw at the start of its turn. If the creature does so, it can't see the medusa until the start of its next turn, when it can avert its eyes again. If the creature looks at the medusa in the meantime, it must immediately make the save.
If the medusa sees itself reflected on a polished surface within 30 feet of it and in an area of bright light, the medusa is, due to its curse, affected by its own gaze.
Normal and giant snakes are immune to the Legendary medusa's gaze.

Actions

Multiattack: The medusa makes either three melee attacks – one with its snake hair, one with its short sword and one constrict – or two ranged attacks with its longbow.

Snake Hair: Melee weapon attack. +5 to hit, reach 5ft., one creature. Hit 4 (1d4+2) piercing damage plus 14 (4d6) poison damage,

Shortsword: Melee weapon attack. +6 to hit, reach 5ft., one creature. Hit 6 (1d6+3) piercing damage.

Constrict: Melee weapon attack. +5 to hit, reach 10ft., one creature. Hit 10 (2d6+3) bludgeoning damage, and the target is grappled (escape DC 13). Until this grapple ends, the target is restrained, and the medusa can't constrict another target.

Longbow: Ranges weapon attack. +5 to hit, range 150/600 ft., one target. Hit 6 (1d8+2) piercing damage plus 7 (2d6) poison damage.

Legendary Actions

The medusa can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The medusa regains spent legendary actions at the start of its turn.

Constrict: The medusa makes one constrict attack.
Bow: The medusa makes one longbow attack
Suggestion (3 actions); The medusa casts the Suggestion spell as an innate spell.

Medusa Lairs

Medusa live forever in seclusion, alienated from the world around them by their monstrous form and caprice. Their homes gradually fall into disrepair until they are little more than shadowy ruins covered with thorns and creepers, riddled with obstructions and hiding places. These hiding places are riddles with serpents attracted by the medusa's presence. Foolhardy looters and adventurers who enter are often unaware of the medusa until the creature is among them. The medusa removes any reflective surfaces from its lair. Statuary of petrified animals and humanoids are scattered throughout the lair, captured in poses of dread.

Lair Actions

On iniative count 20 (losing initiative ties), the medusa can take a lair action to cause one of the following magical effects: the medusa can't use the effect again until it finishes a short or long rest.

1. The medusa uses its rattle to rouse the snakes in its lair. Each creature within 60 feet of the medusa is attacked by a poisonous snake that emerges to bite them and then darts back under cover.

2. The vegetation and collapsed masonry of the medusa's lair impedes all creatures within the lair. All of the lair counts as difficult terrain for the rest of the encounter – the medusa is not affected. Furthermore, creatures must make a DC 13 Dexterity saving throw or have their movement halted until the end of the medusa's next turn.

3. Shrieks of terror suddenly erupt from the mouths of the medusa's previously petrified victims. All creatures must make a DC 13 Intelligence saving throw or be Frightened. On a failure, a creature may make another saving throw on its subsequent turns, success ending the effect.

Regional Effects

The temperature within 600 feet of the lair is several degrees higher than the surrounding area.

There are noticeably more snakes and reptiles within 600 feet of the lair than in the surrounding area.

Birds avoid the area within 600 feet of the medusa's lair.

All of the above effects end within 1d6 days of the medusa's death.

Whoah. Lair action #3 is freakin' awesome!

I'm so gonna use this in my current 5e Ancient Greece campaign. Thanks!

Glad you likey!

I've also rummaged up a picture for those not familiar with what i'm after.

Nice! I didn't quite realize how much I was missing a legendary Medusa, but I think I must have totally needed one after all.

Quote from: LibraryLass;788884Nice! I didn't quite realize how much I was missing a legendary Medusa, but I think I must have totally needed one after all.

Everyone needs a legendary Medusa!

This is neat-o. Thanks for sharing!